(CNN) -- A Red Cross worker was killed Wednesday during shelling in the conflict zone in Sri Lanka, the third aid worker killed in six weeks, the International Committee of the Red Cross says.

A photo supplied by a humanitarian group on Sunday shows civilians allegedly injured in government shelling.

The worker, identified as Majurin Sivakurunathan, was killed along with his mother during an assault, a ICRC spokeswoman said.

The fighting between the Sri Lankan troops and the rebel Tamil Tigers has intensified in the conflict area to the point that the ICRC can not get food to that area or help the sick and wounded, said Sarasi Wijeratne, a ICRC spokeswoman.

The latest death comes after Sri Lanka angrily rebuked a U.N. official Tuesday over remarks by the organization that a civilian "bloodbath" had occurred in the north of the country.

U.N. spokesman Gordon Weiss told CNN on Monday that hundreds of civilians died during weekend fighting because the Sri Lankan army had surrounded rebel fighters in the country's north, putting residents in the crossfire.

The Foreign Ministry expressed its displeasure to Amin Awad, acting resident representative of the United Nations in Sri Lanka, about the comments.

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Mahinda Samarasinghe, Sri Lanka's minister of disaster management and human rights, initially said Weiss would be summoned to explain his remarks, but this did not happen because of diplomatic protocol, a source told CNN, noting that he is a junior official at the U.N. office in Colombo.

Rebel claims of civilian deaths have been considerably higher than those provided by the U.N. Lawrence Christy, the head of the Tamils Rehabilitation Organization, said more than 3,200 civilians died in fighting from Sunday evening until Monday morning, the rebel Web site TamilNet reported. Watch frustration build at the United Nations »

The Sri Lankan government has denied the allegations and accused the Tamils of "taking the whole world for a ride with its well-engineered propaganda ploys," while turning their weapons on civilians trying to flee the combat zone.

Tamil Tiger rebels have been fighting for an independent state in Sri Lanka's northeast since 1983.

As many as 70,000 people have been killed since the civil war began, and the Tigers have been declared a terrorist organization by the European Union and more than 30 countries, including the United States.